Apparatus for thermal decomposition of sludges



H. MILEY March 22, 1960 APPARATUS FOR THERMAL DECOMPOSITION OF SLUDGESFiled Dec. 9, 1954 5 Sheets-Sheet l i it? INVENTOR HUNTER MILEY BY H v2' ATTORNEYS March 22, 1960 H. MILEY 2,929,689

APPARATUS FOR THERMAL DECOMPOSITION 0F SLUDGES Filed Dec. 9, 1954 3Sheets-Sheet 2 INVENTOR HUNTER MILE V ATTORNEY;

H. MILEY APPARATUS FOR THERMAL DECOMPOSITION 0F SLUDGES Filed Dec. 9,1954 3 Sheets-Sheet 3 1 N VEN TOR HUNTER MILE) BY fg x ATTORNEY:

United States Patent Hunter Miley, Petrolia, Pa., assignor to L.Sonneborn Sons, Inc., a corporation of Delaware Application December 9,1954, Serial No. 474,256

10 Claims. (Cl. 23-261) This invention relates to improvements in thethermal decomposition of sludges and is a continuation in part of myco-pending application, Serial No. 314,605, filed October 14, 1952, andnow abandoned.

The invention more particularly relates to improvements in the thermaldecomposition of sludges,.produced in the treatment of hydrocarbon oilswith sulfuric acid, to recover the sulfur content of the same in theform of sulfur dioxide. 1

The oils referred to may, for example, be petroleum distillates orpetroleum residues, overhead cuts derived from the distillation of coaltars, or hydrocarbon oils produced synthetically by hydrogenation or bythe Fischer-Tropsch process. In the course of purifying such oils tomeet market specifications, they are treated in liquid phase with strongsulfuric acid to remove those constituents which are most easily reactedwith the acid. Where a mild treatment only is desired, the acid mayrange from 93 to 98%, but where a more rigorous treatment is required,as, for example, in the manufacture of technical and medicinalwhiteoils, fuming acid or sulfuric anhydride is employed. The expressionsulfuric acid as used in the claims includes sulfuric anhydride. Aftersuch treatment, the reaction mass stratifies, with the treatedhydrocarbon oil above and with a sludge layer below. The sludge layercontains products of the reaction between the sulfuric acid and thehydrocarbons together with unreacted sulfuric acid. These sludges arefound in varying degrees of fluidity, depending on the type andcharacter of hydrocarbon reacted and the amount of residual sulfuricacid present. Various methods have been described in the prior art forthe treatment of such sludges to recover the major part of the sulfurpresent in the form of sulfur dioxide.

One object of this invention is an improvement over all such knownsludge-treating methods which will allow the obtaining of a moreconcentrated sulfur dioxide and a firmer coke containing only relativelysmall amounts of residual sulfur. This, and still further objects, willbecome apparent from the following description readin conjunction withthe drawing, in which:

Fig. 1 is a diagrammatic showing of an embodiment of an apparatus foreffecting the thermal decomposition of sludges in accordance with theinvention;

Fig. 2 is a plan view showing the conveyor mixer of the embodiment shownin Fig. 1 with the casing partially cut away;

Fig. 3 is a diagrammatic showing of a further embodiment of an apparatusfor decomposing heavier or oilier sludges in accordance with theinvention;

Fig. 4 is a diagrammatic showing of still a further embodiment of anapparatus for decomposing oilier or heavier sludges in accordance withthe invention; and

Fig. 5 is a diagrammatic section through the roto lift of the embodimentshown.

Referring to the embodiment shown in Fig. 1 of the drawing, 1 designatesa horizontal worm conveyor driven 2,929,689 Patented Mar, 22,

. 2 by any suitable means diagrammatically indicated by 2. Worm conveyor1 is mounted in tubular housing 3 and operates to move granular materialin the direction indicated by arrow 4, discharging it by gravity into abank of vertical pipes 5, and discharging any excess over that carriedaway by these vertical pipes, into the outlet 6. A grizzly 31 ispositioned directly below the worm conveyor 1 at the portion directlyabove the bank of vertical pipes 5 so that any oversize particles orlumps will not discharge into the bank of pipes which might tend to clogthe same. Additionally, a vibrator 32 of any known or conventionalconstruction is connected to the side wall of the casing adjacent theinlet to the vertical pipes 5. The vibrator 32 insures an even andsmooth flow of the materials into the vertical pipes, and addi tionallyprevents clogging. The vertical pipes 5 in turn discharge intofunnel-shaped hopper 7, discharging into tubular casing 8. Within thecasing 8 there is provided the horizontally disposed conveyor mixer 9..The conveyor mixer 9 consists of a conveyor having two par.- allelrotatably mounted worm shafts 11 driven in the same direction by themotor 12. The worm blades 10 of each shaft 11 have the same direction ofpitch and mesh with each other. With this arrangement a very excellentmixing and conveying is eflected and the in termeshing, similarlyrotating worms are self-cleaning, thus preventing any clogging. In orderto increase the capacity, it 'is also possible to use additional worms,as, for example, three worms equally spaced from each other in a housingof triangular cross-section. The worms may also, of course, haveopposite pitches and rotate in opposite directions. Casing 8 is providedwith vent 13, through which gas may be taken off. Any gas accumulatingin housing 3 may be withdrawn through pipe 13. Casing 8 is also providedwith pipe 14, through which sludge may be introduced to be incorporatedby the conveyor mixer 9 with solid particles contained in the casing 8.The conveyor mixer 9 moves the body of particles 15 within the casing 8toward the discharge outlet 16 oriented downwardly at an angle of about45. The discharge outlet passes the material into the lower end oftubular casing 17, which contains a so-called roto lift 18. This rotolift consists of a conveyor in the form of an Archimedian spiral 19wound upon the shaft 21, which, in turn, is driven by any suitable meansdiagrammatically indicated by '22. The shaft 21 is operated at a speedsufficiently high to insure that any particles within the casing 17 willbe thrown outwardly by centrifugal force'and will'therefore hug theinner wall of the casing 17. The operation of the roto lift is thereforesimilar in principle to that of th'e ordinary worm conveyor exceptingthat, since centrifugal force is substituted for gravity, it can operateto move material upwardly; and, whereas in the ordinary worm conveyor,the materials tend to accumulate by gravity in the base of .the housing,in the roto lift they are uniformly distributed over the entire interiorof the housing. From the upward end of the roto lift the materials aredischarged into the duct 23 oriented downwardly at an angle of about 45and discharging into the intake end of housing 3, which contains theworm' conveyor 1.? 25 diagrammatically indicates a furnace of anysuitable type, in which hot gases, such as, for example, gaseousproducts of combustion, are generated, passing therefrom through theduct 26 into the housing 27, which surrounds the bank of vertical pipes5. From the upper end of housing 27 these gases pass through horizontalduct 28 into the vertically disposed housing 29, by which they aredownwardly directed around the outer surface of casing 17, to beeventually discharged through duct 30 communicating with a suitablestack not shown,

duced in the operation of the process. Such coke should" have a maximumsize of about 4 mesh-and preferably of about 10 mesh. The actual size isnot critical, since it will eventually be displaced by the coke producedin the operation of the process, the particle sizeof which is deftermined by'the processitselfi] Following this, the heater 25-is'started in operation. As will be noted, the hot combustion gases movegenerally counter-current to the solid material, with the result thatthe solid material will have a maximum temperature at the lower end ofthe vertical pipes 5 and the funnel-shaped hopper 7. Whenever the solidparticles at this point have attained a temperature in excess of thedecomposition temperature for .at anvpoint, and all of the materialsoverflowing at 6 i may be diverted for either of these'purposes.

theparticular sludge to be treated, the process maybe within-the-rangeof from 350-450 F., depending upon the characteristics of the particularsludge, and the vol ume of sludge introduced is coordinated withthe'tem- .perature of the particles at 7 to produce. a mixture which isat leastat'the temperature ofdecomposition of the sludge and notexceeding 500 F. Preferably, the'teniper-ature of the mixture does notexceedthe decomposh tion temperature ofthe sludge treated by more than50? I usually operate within the range "of from 350- r set in operationby the introduction of sludge through the inlet 14. This sludge isimmediately mixed into the 450 F. To insure smooth and successfuloperation, the

masslof the solid particles moving through 7 should be iat least 5times, andv preferably 10 times, the mass of the sludge introducedthrough 14. a The heating effect is immediate and uniform' and resultsin the almost immediate decomposition of the sludge to produce sulfuriiifixide in gas phase without any substantial release of {thehydrocarbon content of the sludge. -I am therefore able in this way toproduce a sulfur dioxide gas containinjgjat least 98% sulfur dioxide byvolume, with only .a traee of hydrocarbons. tiaily complete by the timethe particles reach the duct l6! At this point, owing tothe heatcapacity of the sludge and the energy consumed in its decomposition, themoving stream of particles which are entirely free from any apparentliquid material, will be at a temperature within the range of from300-430 F., and preferably about 330 F. As the particles are movedupwardly by the roto lift 18, part of this heat is restored, "and by thetime the particles have moved downwardly.

in the bank'of vertical pipes 5 into the hopper 7, they ag'ainhave beenbrought to a temperature sufficiently in excess of the decompositiontemperature of the sludge, so that, after mixing with the incomingsludge in the casing 8, the mixture will again be at a temperature inexcess of the decomposition temperature of the sludge and preferablywithin the range of from 350-450 F.

Shortly after the start of operations, solid material will begin tooverflow from the outlet 6. This is due to the increased mass ofmaterial within the system, resulting from the residual hydrocarbonsintroduced with the in coming sludge. Eventually, ofcou'rse, theoriginal particles introduced when starting up will be entirelydisplaced, with the result that this material is composed entirely ofcoke'parti'cles produced in the system by. the decomposition of thesludge. These particles are diverted from the system either for use 'asfuel or for metallurgical purposes. If the original particles suppliedto the system were coke, 'it would not bemcessary to cut stream Thedecomposition is substan- When using the above-descr bed arrangementwith the so-called heavy or oily sludges,'it has been found that theviscous or oily or tarryhydrocarbons will accumulate and build up in thecontinuously circulating body of coke, eventually clogging the device.In accordance witha preferred embodiment of my invention for thedecomposition of these heavy or oily sludges with the recovery of thesulfur values, I drive'off at least a portion. of these hydrocarbonsfrom thecirculating bodyof coke at some point in the cycle, so that adry coke is produced and maintained in"circulati'on. This driving oft ofthe hydrocarbons from the coke may be effected in various ways.

It has been found preferable to allow the hydrocarbon vapors to escapefrom the coke after the same has passed through the tubes 5 of the heatexchanger 7 and prior to the mixing ofthc coke with the sludge.

This may beaccomplished, for example, by raising the tube plate 33 toprovide a free space above the'body of coke emerging from the tubes Sanda free surface for the escape of the hydrocarbon vapors. These, vapors,which escape into this. free, space, may be removed through any suitableconduit,'and, for example, may be recovered or burned in the contactpurification furnace of the plant. Advantageously, these vapors may bepiped from this free space below the raised tube plate to the spaceabove the tube plate surrounding the tubes in thefheat .exchanger, wherethe same may at least partially burn with the combustion gases passedfrom the combustion cham her or heater 25, thus supplying additionalheat to heat the downwardly moving body. of coke. V r

Such an arrangement is shown in Fig. 3. In this embodiment the tubePlate 33 is raised to provide a free surface on the body of cokeemerging from the tubes 5 and a free space above thissurface throughwhich the oil vapors can escape." A conduit 34 connects this free spacebelow the tube plate 33 to the space in the heat exchanger 27 above. thetube ,plate 33 surrounding the tubesS. J i a a It has been foundpreferable to provide a recirculation system for the thus-removed oil:vapors to :theburner 25. shown, the combustion gases, along with theremoved oil vapors, pass out of the heat exchanger7 into and through thehousing 29, where the same, by indirect heat exchange, heat the materialbeing lifted in the roto lift -17, and through the duct '30to the stack37. Also connected to the stack 37 is a conduit 38, a blower 39, and aconduit 40, connecting the blower 39with the combustion chamber 25. Theblower 39 sucks at least a portion of the ,gases andoil vapors from thestack 37 and forces the same into the combustion chamberZS. In

the combustion chamber 25 the quantity of oxygen in the'form of airintroduced through 35 may be so controlled as to cited completecombustion of the fuel introduced and these oil vapors. gases which thenpass through the heat exchanger 27, do not contain suflicient excessoxygen to burn the oil vapors from the conduit 34. The combustionprocess and the burning of the removed oil vapors may thus be controlledby theamount of air introduced through35, so that the correctand desiredtemperature is maintained. By burning the recycled oil,vapor's,atheamount of'fuel, .such as natural gas introduced through 36, may be cutby more than half. v V V In .all votherrespects, the construction andoperation of the embodiment shown in Fig. 3 .is identical to that shownin Figs. 1 and 2. By the removal of the .oil vapors in this manner,however, the heavier andoilier sludges maybe satisfactorily handled. t

)In the embodiment shown in Fig. 4, the oil vapors are removed byeliminating the bottom tube plate 33 altogether, therebyproviding apath'ofescapefor the oil The hot combustion vapors directly up into theheat exchanger 27 and throw.-

from the tubes. The removed oil vapor is then recycled and burned in themanner identical to that described in connection with Fig. 3. The directsurface contact of the coke as it emerges from the tubes with the hotcombustion gases has been found to very materially aid in the eificientremoval of the oil which might tend to accumulate in the circulatingbody of coke and clog the same.

Additionally, it has been found preferable, in order to produce a cokecontaining less volatile material, to pass a stream of anoxygen-containing gas, such as air, up through the downwardly movingbody of coke, as the same emerges from the tubes 5.

As shown in Fig. 4, air is piped from the air inlet 35 through theconduit 41 to below a hollow, conicallyshaped member 42, which ispositioned below the exit of the tubes 5. This conical member hasnotches or serrationsal'ong its edges. Thus, for example, with a cone ofabout 24 inches indiametenserrations about 1 inch high, /2 inch acrosstheir lower edges, spaced 1 inch apart, may be used. The cone controlsthe flow of the coke out of the tubes 5 and insures an even contact withthe air which flows up through the notches with the coke. This aircauses a superficial oxidation of the coke particles and materially aidsin the removal of the undesirable volatile matter which may causeclogging in the system.

In this embodiment, the worm 19 of the roto lift 17, as may best be seenin Fig. 5, is tapered at the bottom. Very surprisingly and unexpectedly,the use of this tapered screw construction more than doubles thecapacity of the lift. In all other respects, the construction andoperation of the embodiment shown in Fig. 4 is identical to thatdescribed in connection with Figs. 1, 2, and 3.

Though in the embodiment shown in Fig. 4, there is some direct contactof the coke particles with the hot combustion gases and some oxidationof the coke particles which necessarily results in a heating of theparticles, the main heating of the coke particles for the sludgedecomposition is an indirect heating in the heat exchanger 27. When anindirect heating of the moving body of coke particles is recited hereinand in the claims, the same is specifically intended to designate thismain heating and not to exclude the additional direct heat contact andoxidation for the removal of the hydrocarbon vapors.

The removal of the hydrocarbon vapors, as indicated in the embodimentsshown in Figs. -3 and 4, will not result in any contamination of thesulfur dioxide, since over 97% of the sludge is decomposed by the hotcoke in the conveyor mixer 9 and the remahiing small percent in the rotolift 17. This residual small sulfur dioxide content which is notrecovered through the outlet 13 is recovered through the outlet 13'.

While in the embodiments in which the hydrocarbons are separated fromthe circulating body of coke at a point in the cycle, the body of cokemay be heated at one point in the cycle to a relatively highertemperature to facilitate the removal of the vapors, as, for example, atemperature of about 630700 F. at the exit of the heat exchanger 27,this higher temperature has not been found to be necessary. It has beenfound that optimum results are obtained if the temperature of thecirculating body of coke does not exceed a temperature above 500 F. atany point in the cycle. Thus, for example, in the embodiments shown inFigs. 3 and 4, the temperature of the coke at the exit of the heatexchanger 27 is preferably maintained at about 440-470 F. with atemperature of the heating gas of about 1300-1400 F. in the heatexchanger.

The coke is in all cases mixed with the sludge to pro- ,6 .duG a mixtureof at least th decomposition temperature of the sludge and not exceeding500KB. It has b'egn found preferable to operate so that the mixture ofcoke and sludge is at a temperature of about 400- 430 F., and thistemperature is maintained in the cycle until the coke re-enters the heatexchanger tubes.

' It may be noted that the drop in temperature when the sludge is addedis only about 40, so that an isothermal condition for the circulatingbody of coke is substantially approached. Even with this small change'of temperature in the circulating body of coke, all of the hydrocarbonswhich would cause the circulating coke body to become oily and clog, areremoved.

In the preferred embodiment of my process, with or without the removalof hydrocarbons, the mass of carrier particles circulating within thesystem is at least 15 times the mass of the sludge supplied to thesystem. This has two important and valuable results, i.e., thetemperature of the particles at 7 and just before mixing with the sludgeneed only be very slightly higher than the decomposition temperature ofthe particular sludge, with the result that the decomposition is highlyselective and easily controlled.

substantially vertically extending tubular heat exchanger having aheating gas chamber and a multiple number of tubes therethrough for thegravity flow of coke particles, a conveyor mixer within said conduitpositioned for conveying coke particles from the lower end of said heatexchanger, a sludge feed inlet to said conveyor mixer, a gas take-01foutlet communicating with said conduit for the removal of decompositiongases from the conduit portion within the conveyor mixing area beyondsaid sludge inlet, a roto lift within said conduit substantiallyextending vertically and positioned for conveying coke particles fromadjacent the far end of said conveyor mixer, and conveyor means withinsaid conduit positioned for passing coke particles from the top of saidroto lift to the top of said heat exchanger for'repassage therethrough,

and means for passing heating gas through said heatinggas chamber ofsaid heat exchanger.

2. Device according to claim 1, in which said roto lift has asubstantially vertical conveyor worm tapered in an upward direction atits lower end portion.

3. Device according to claim 2, including means for passing heating gasfrom said heating-gas chamber in heat-exchange relation to at least aportion of the remainder of said conduit substantially counter-currentto the direction of travel of material within said conduit.

4. Device according to claim 1, in which said heating gas chamber is ingas-flow communication with the portion of said conduit therebelow, andin which said means for passing heating gas through said heating chamberincludes a combustion chamber, and including means for recycling atleast a portion of the gases from said heating gas chamber to saidcombustion chamber.

5. Device according to claim 4, in which said heating chamber is in freecommunication with the portion of said conduit therebelow, and includingmeans for passing a combustion-supporting gas into said conduit belowsaid tubes.

6. Device according to claim 5, including a conically shaped memberhaving serrated edges positioned below said tubes and in which saidmeans for passing for said combustion-supporting gas comprises a conduitterminating below said conically-shaped member.

7 7 said conveyor mixer, a gamakeifibuflet mm; m 'u iicming V 71,339,519 17 2 9 asm 2,395,503

References 'Cited in the filefof'this l ate'nif V I FOREIGN PA ENTS I r7 Netherlands"; Mar. -15, 19 50

1. DEVICE FOR THERMALLY DECOMPOSING SULFURIC ACID SLUDGES, WHICHCOMPRISES MEANS DEFINING A SUBSTANTIALLY ENCLOSED ENDLESS CONDUIT FORTHE CONTINUOUS CIRCULATION OF A BODY OF COKE PARTICLES THERETHROUGH ANDINCLUDING A SUBSTANTIALLY VERTICALLY EXTENDING TUBULAR HEAT EXCHANGERHAVING A HEATING GAS CHAMBER AND A MULTIPLE NUMBER OF TUBES THERETHROUGHFOR THE GRAVITY FLOW OF COKE PARTICLES, A CONVEYOR MIXER WITHIN SAIDCONDUIT POSITIONED FOR CONVEYING COKE PARTICLES FROM THE LOWER END OFSAID HEAT EXCHANGER, A SLUDGE FEED INLET TO SAID CONVEYOR MIXER, A GASTAKE-OFF OUTLET COMMUNICATING WITH SAID CONDUIT FOR THE REMOVAL OFDECOMPOSITION GASES FROM THE CONDUIT PORTION WITHIN THE CONVEYOR MIXINGAREA BEYOND SAID SLUDGE INLET, A ROTO LIFT WITHIN SAID CONDUITSUBSTANTIALLY EXTENDING VERTICALLY AND POSITIONED FOR CONVEYING COKEPARTICLES FROM ADJACENT THE FAR END OF DAID CONVEYOR MIXER, AND CONVEYORMEANS WITHIN SAID CONDUIT POSITIONED FOR PASSING COKE PARTICLES FROM THETOP OF SAID ROTO LIFT TO THE TOP OF SAID HEAT EXCHANGER FOR REPASSAGETHERETHROUGH, AND MEANS FOR PASSING HEATING GAS THROUGH SAID HEATING GASCHAMBER OF SAID HEAT EXCHANGER.